The Providence Limestone member of the Dugger Formation in Indiana and its lithologic correlatives in the southern part of the Illinois Basin are thin lime mudstones to packstones lying stratigraphically between the Herrin and Hymera Coal Members of the Dugger Formation and their equivalents. The purposes of the study are to describe and correlate the Providence conodont fauna and to apply biofacies analysis and petrographic study to interpreting the paleoenvironments.
Providence conodonts are dominated by representatives of the Idiognathodus-Streptognathodus plexus. Hindeodus is abundant; Neognathodus is common; and Idioprioniodus, Adetognathus, and Diplognathodus are common only in some sections. Aethotaxis is a minor constituent.
Conodont biofacies reflect a shallow, nearshore, low- to moderate-energy marine environment. The Idiognathodus-Streptognathodus plexus indicates quiet to moderately elevated energy levels. Hindeodus replaces part of the Idiognathodus-Streptognathodus plexus in higher energy conditions. Diplognathodus has an affinity for low to slightly elevated energy conditions. Migration during ontogeny to quite, organic-rich water from a more open, slightly higher energy environment is indicated for Streptognathodus oppletus.
Assignment to the Neognathodus dilatus-N. roundyi zone indicates a middle Desmoinesian age. The new species Diplognathodus indianaensis is morphologically intermediate between the early Desmoinesian D. coloradoensis and the late Desmoinesian D. illinoisensis and allows refinement of a Diplognathodus-based zonation.